arXiv subjects

R. S. Kolodka

Publications and source records attributed to R. S. Kolodka.

5 recordsLinked to original sources

arXiv2025

Features of Surface Structuring of Direct and Indirect Band Gap Semiconductors by Femtosecond Laser

The impact of femtosecond (fs) laser radiation on semiconductors with direct (ZnSe, GaAs, CdZnTe) band gap, with the structurally induced direct-to-indirect band gap transition (PbI2, GaSe) and indirect band gap (Si) has been studied. The fs-laser treatment of semiconductors has been performed in the multi-pulse regime in air environment. The influence of fs-laser radiation parameters on surface morphology of the semiconductors has been analysed by scanning electron microscopy (SEM) and 2D Fourier transform of SEM images, optical photoluminescence spectroscopy. Under the treatment with the fundamental fs-laser radiation (800 nm, about 130-150 fs) both low spatial frequency LIPSS and high spatial frequency LIPSS have been observed. Specific features of LIPSS of two types (low spatial frequency LIPSS and high spatial frequency LIPSS) and other structure peculiarities (grooves, grains, different defects in periodic structure, i.e. loops, strip breaks, and ablation products) have been also analysed. The formation mechanisms of LIPSS are also considered within the scope of two approaches,namely an electromagnetic approach and matter reorganization processes.

physics.optics↗

arXiv2010

Optical initialization, readout and dynamics of a Mn spin in a quantum dot

We have investigated the spin preparation efficiency by optical pumping of individual Mn atoms embedded in CdTe/ZnTe quantum dots. Monitoring the time dependence of the intensity of the fluorescence during the resonant optical pumping process in individual quantum dots allows to directly probe the dynamics of the initialization of the Mn spin. This technique presents the convenience of including preparation and read-out of the Mn spin in the same step. Our measurements demonstrate that Mn spin initialization, at zero magnetic field, can reach an efficiency of 75% and occurs in the tens of \emph{ns} range when a laser resonantly drives at saturation one of the quantum dot transition. We observe that the efficiency of optical pumping changes from dot to dot and is affected by a magnetic field of a few tens of mT applied in Voigt or Faraday configuration. This is attributed to the local strain distribution at the Mn location which predominantly determines the dynamics of the Mn spin under weak magnetic field. The spectral distribution of the spin-flip scattered photons from quantum dots presenting a weak optical pumping efficiency reveals a significant spin relaxation for the exciton split in the exchange field of the Mn spin.

cond-mat.mes-hall↗

arXiv2009

Towards coherent optical control of a single hole spin: Rabi rotation of a trion conditional on the spin state of the hole

A hole spin is a potential solid-state q-bit, that may be more robust against nuclear spin induced dephasing than an electron spin. Here we propose and demonstrate the sequential preparation, control and detection of a single hole spin trapped on a self-assembled InGaAs/GaAs quantum dot. The dot is embedded in a photodiode structure under an applied electric-field. Fast, triggered, initialization of a hole spin is achieved by creating a spin-polarized electron-hole pair with a picosecond laser pulse, and in an applied electric-field, waiting for the electron to tunnel leaving a spin-polarized hole. Detection of the hole spin with picosecond time resolution is achieved a second picosecond laser pulse to probe the positive trion transition, where a trion is created conditional on the hole spin to be detected as a change in photocurrent. Finally, using this setup we observe a Rabi rotation of the hole-trion transition that is conditional on the hole spin, which for a pulse-area of $2π$ can be used to impart a phase-shift of $π$ between the hole spin states, a non-general manipulation of the hole spin.

cond-mat.mes-hall↗

arXiv2008

Fast optical preparation, control and read-out of single quantum dot spin

We propose and demonstrate the sequential initialization, optical control, and read-out of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent read-out of the hole spin state.

cond-mat.mes-hall↗

arXiv2006

Nuclear Spin Switch in Semiconductor Quantum Dots

We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a threshold-like enhancement or reduction of the local nuclear field by up to 3 Tesla can be generated by varying the intensity of light. The excitation power threshold for such a nuclear spin "switch" is found to depend on both external magnetic and electric fields. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of spin transfer from electrons to the nuclei of the dot.

cond-mat.mes-hall↗